In common channel signaling networks, such as SS7 networks, adjacent nodes in a network are connected by signaling links. Signaling links are transmission lines that carry signaling messages between the adjacent nodes. For reliability and load sharing purposes, multiple signaling links may connect two adjacent nodes. Groups of signaling links that connect the same two adjacent nodes are referred to as signaling linksets.
FIG. 1 illustrates the signaling link and linkset concepts. Referring to FIG. 1, an SS7 service switching point 100 is connected to another SS7 service switching point 102 via a signal transfer point 104. In an SS7 network, service switching points perform call signaling functions and provide voice trunks for carrying media stream communications between end users. Signal transfer points route signaling messages between SS7 signaling points.
In the illustrated example, service switching point 100 is connected to signal transfer point 104 by four signaling links 106, 108, 110, and 112. Similarly, service switching point 102 is connected to signal transfer point 104 by signaling links 114, 116, 118, and 120. Signaling links 106, 108, 110, and 112 form a linkset 122. Similarly, signaling links 114, 116, 118, and 120 form another linkset 124.
When routing messages from SSP 100 to SSP 102, STP 104 must select one of signaling links 114, 116, 118, and 120. Such selection is preferably performed so that messages are evenly distributed on signaling links 114, 116, 118, and 120. In ANSI and ITU networks, signaling messages include a signaling link selection (SLS) parameter used to select the appropriate signaling link for outbound signaling messages. In ITU networks, the SLS value is 4 bits. For ITU ISUP messages, the SLS is also the lower 4 bits of the CIC.
FIG. 2 illustrates a routing label 200 of an ITU ISUP message. ISUP messages are sent between SSPs to set up and tear down calls. The routing label is a portion of a message storing information used by signal transfer points to route the message. In FIG. 2, routing label 200 includes an originating point code field 202, a destination point code field 204, and a circuit identifier code (CIC) field, including an SLS portion 206 and other CIC bits 208. OPC field 202 stores the point code of the node that originated the ISUP message. For example, in the network illustrated in FIG. 1, OPC field 202 will store the point code of SSP 100 for ISUP messages originated by SSP 100. DPC field 204 stores the destination point code of the ISUP message. Again using the example in FIG. 1, if a message is destined for SSP 102, DPC field 204 will store the point code of SSP 102. The CIC field is used to store an identifier for the circuit used to carry voice traffic. Portion 206 of the CIC field is used in ITU networks as a signaling link selection code. Other CIC bits portion 208 (bits 5–16) has not been used for signaling link selection.
One problem with using bits of the CIC code to perform signaling link selection in international networks is that one or more of the CIC bits may be fixed, which reduces the number of bits remaining for signaling link selection. For example, ITU-T Recommendation Q.764, SS7-ISDN User Part Signaling Procedures, September 1997, states that a service switching point can use either all odd or all even CICs to reduce glaring, which is a problem that occurs in telecommunications networks when two SSPs attempt to seize the same trunk at the same time. Since the CIC identifies the voice trunk, in order for an SSP to use all odd or all even trunks, the least significant bit of the CIC code is fixed. As a result, bit 16 of SLS sub-field 208 illustrated in FIG. 2 is also fixed. Because this bit is fixed, conventional signaling linkset and link selection algorithms that have relied on these four bits to select signaling links or linksets will result in unbalanced load sharing. Therefore, there exists a need for improved methods and systems for signaling link and linkset selection in international networks.